The invention relates to composite containers, and in particular relates to composite containers for vacuum packaging expansible food products, such as dough products, and associated methods.
Food and drink products and other perishable items are often packaged in tubular composite containers that are sealed at both ends. These composite containers typically include at least one structural body ply made of paperboard and are formed by wrapping a continuous strip of the body ply material around a mandrel of a desired shape to create a tubular structure. The body ply strip may be spirally wound around the mandrel or passed through a series of forming elements so as to be wrapped in a convolute shape around the mandrel. At the downstream end of the mandrel, the tube is cut into discrete lengths and fitted with end caps to form the container. Tubular containers of this type typically include a liner ply on the inner surface of the paperboard body ply. The liner ply prevents liquids from leaking out of the container and also prevents liquids from entering the container and possibly contaminating the food product contained therein. Preferably, the liner ply is also resistant to the passage of gasses so as to prevent odors of the food product in the container from escaping and to prevent atmospheric air from entering the container through the liner and spoiling the food product. The liner ply is often a laminate including kraft paper, aluminum foil and/or one or more polymer layers. Thus, the liner ply provides barrier properties and the body ply provides structural properties for the composite container.
xe2x80x9cEasy-openxe2x80x9d Containers for Expansible Food Products
Composite containers for packaging products under pressure, particularly refrigerated dough products, constitute a significant commercial consumer product. The pressure is caused by the dough expanding after it has been packaged. The leavening of the dough, also known as rising or xe2x80x9cproofing,xe2x80x9d causes the generation of byproduct gasses, primarily carbon dioxide, which outgas from the dough into any surrounding air pockets or headspace. The byproduct gasses also build up within the dough itself which causes expansion of the dough. The proofing thus places outward pressure on the container and can create concerns of premature opening of the container.
To obtain easy consumer openability of these types of dough containers, the body wall is intentionally designed to provide little circumferential strength and thus the body ply strip is often joined at its edges by a butt joint that is lightly adhered or not even adhered at all. This facilitates opening of the container by first removing the label and then striking the tubular body wall against a hard and relatively sharp surface, such as the edge of a kitchen countertop, to separate the body ply edges and obtain access to the food product therein. The outer label surrounding the butt joint in containers of this type is thus an important structural component of the container because the outer label bridges the butt joint and maintains it in a closed position. Accordingly, the label must have sufficient circumferential strength to prevent premature opening of the container. On the other hand, once the label is removed, the seam of the body ply should be fairly easily separated to allow the consumer to gain access to the product.
Commercially significant containers of this type are disclosed in U.S. Pat. No. 3,981,433 to Thornhill, et al. which is directed to an xe2x80x9ceasy-openxe2x80x9d container including an inner liner having a helical fold positioned opposite the helical butt joint. When the outer label is removed, the dough and the liner expand outwardly together as the liner fold or pleat begins to unfold. Resultant pressure on the body ply material causes the butt joint to open. This in turn allows the inner liner to expand further such that the liner is automatically opened by the rapidly expanding dough to allow access to the dough in the interior of the container by the consumer.
A complaint of some consumers of expansible dough products is that conventional easy-open dough containers create a loud report or xe2x80x9cpopxe2x80x9d when the container is first opened. The loud report can startle some consumers and is caused by the rapid decompression of the container upon opening. Accordingly, one goal of easy-open container manufacturers is to provide a container having a much quieter report upon opening.
Containers for Vacuum Packaging
Certain food products benefit from being packaged while under a vacuum. Vacuum packaging removes oxygen from the space surrounding the product, which can improve the shelf life of the product within the package. However, it is generally recognized that vacuum packaging with the easy-open containers of the butt joint type can only be accomplished with difficulty, if at all. Because of the structural design of the composite container, the application of vacuum to the interior of the container often results in partial or complete inward collapsing of the container walls along the butt joint seam. This can result in an unacceptable appearance for the composite container or an unacceptable sealing of the product within the container.
This problem is further discussed in U.S. Pat. No. 5,251,809 to Drummond, et al. The dough container according to one embodiment of the ""809 patent has an overlapping joint or seam between the opposing edges of the body wall material formed by compressing marginal areas of the body ply material to a thickness which is less than the original thickness of the paperboard. A frangible adhesive is applied between the compressed overlapping edges such that the joint can be easily opened with an appropriate amount of pressure. Because of the strength imparted by the overlapping edges and frangible adhesive, the structural strength requirements for the outer label can be decreased without compromising the ability of the container to withstand the vacuum packaging operation.
Another approach to solving the problem of being able to vacuum package expansible food products such as dough is disclosed in U.S. Pat. No. 5,084,284 to McDilda, et al. The McDilda patent discloses a spiral wound composite container in which refrigerated dough can be packaged under a vacuum. As noted in the McDilda patent, the container is adapted to be opened by the application of an external force to the outer surface of the container yet is strong enough to withstand a vacuum environment during packaging of the dough. This is accomplished in the ""284 patent by way of an angled skive joint between the opposed edges of the body ply. The skive joint has an included angle of about 3.5xc2x0 and is held together with an adhesive, such as a dextrose and water combination. This joint is much stronger than conventional dough containers, so much so that the ""284 patent explains that the body ply is sufficiently strong to prevent premature opening of the container and that, therefore, the label layer does not function to add circumferential strength. Unfortunately, the stronger body ply joint also makes it more difficult for the consumer to open the container and gain access to the product after the label ply has been removed.
Accordingly, there is a great need in the industry for a container that is easy to open for consumers, but that is also capable of allowing vacuum packaging of expansible food products. Such a container would advantageously not generate a loud report or pop upon opening and would not involve great difficulty in opening so as to be more friendly to consumers. At the same time, however, such a container would also be capable of withstanding the rigors of vacuum packaging so as to increase the shelf life of the product and provide other benefits attendant to vacuum packaging. Conventional containers, as shown above, have been unable to provide easy openability with vacuum packaging capability and the industry is in need of such a container.
These and other advantages are fulfilled by a tubular container for expansible food products according to the present invention which includes a flexible liner having opposed end portions secured to respective ends of a tubular body wall. Advantageously, the flexible liner has a free medial portion between the end portions that moves inwardly against the expansible food product when a vacuum is applied during packaging and that also then moves outwardly against the inner surface of the tubular body wall as the product expands. In this manner, the vacuum created during packaging does not act directly on the body wall thus allowing conventional easy opening body wall constructions for expansible food products to be used. A further advantage is that the report upon opening is much less relative to conventional containers because, as explained in more detail below, part of the expansion of the packaged food product is taken up by the outward expansion of the liner. As a result, the final pressure within the container, and thus the loudness of the report upon opening, are greatly reduced.
In particular, the tubular body wall has opposed ends and inner and outer surfaces and comprises a wound strip of material having opposed side edges. The strip is wound such that the opposed side edges are butted adjacent to each other. The butted edges of the strip of body wall material are not necessarily secured to each other.
An end closure is secured to each end of the tubular body wall and can hermetically seal the container. The end closures are, according to one embodiment, formed of a paperboard material. A label surrounds the outer surface of the tubular body wall. The label has a predetermined circumferential strength to at least partially resist expansion of the food product together with the circumferential strength of the body wall.
A vent hole can be formed through the body wall and the label, such as with a laser, for allowing the passage of air therethrough. The vent allows air to enter the cavity between the flexible liner and the inner surface of the tubular body wall and allows the medial portion of the liner to move inwardly against the food product as the volume of the food product is decreased.
The flexible liner is secured to the respective ends of the tubular body wall by way of an adhesive band between the liner and the inner surface of the tubular body wall adjacent each end of the tubular body wall. The free medial portion is between the opposed end portions of the liner. Thus, the medial portion is free to move inwardly against the expansible food product when vacuum is applied and then to move outwardly toward the inner surface of the tubular body wall as the expansible food product begins to expand. The liner preferably comprises a flexible and stretchable liner formed of at least one polymeric layer without foil and paper layers.
Associated methods also form a part of the invention and, according to one embodiment, include the steps of forming a tubular body wall with opposed ends and a flexible liner adjacent an inner surface of the body wall, closing one end of the tubular body wall and then depositing the expansible product within the liner and tubular body wall. The vacuum packaging operation can then be performed by applying a negative pressure to the open end of the tubular body wall such that the flexible liner is moved inwardly from the inner surface of the body wall against the product. The open end of the tubular body wall is then closed. The product then expands such that the flexible liner is moved outwardly towards the inner surface of the body wall and a positive pressure is created within the tubular body wall.
Accordingly, and as is explained in more detail below, the Applicants have provided a new container for expansible food products such as dough which overcomes the disadvantages of conventional containers. The new container is easy to open for consumers, but is also capable of allowing vacuum packaging of dough. The present container does not generate a loud report or pop upon opening because part of the expansion of the dough is taken up by the expansion of the medial portion of the flexible liner. The container can use conventional body wall and label construction techniques, such as a body ply butt joint, and thus involves no greater difficulty in opening for consumers than conventional dough containers. At the same time, however, the present container is capable of withstanding the rigors of vacuum packaging so as to increase the shelf life of the dough and provide other benefits attendant to vacuum packaging.